In drilling for oil and gas, a drilling string of pipe secured together by tool joints having drill collars at its lower end to which a bit is connected is rotated from the surface of the ground to drill a bore hole in the earth to the formation or formations from which oil or gas or both are to be produced. During the course of the drilling operations, a casing having an inside diameter large enough for passage of the drilling string, tool joints, drill collars and bit is secured in place, normally by cementing, to hold the earth formations in place and prevent them from collapsing onto the drilling string and drill collars, and to prevent fluid circulated through the drill string, the drill collar and bit and circulated with earth boring up the annulus between the drill collars, and drill string and the earth and casing to enter the earth formations and to prevent fluid from the formations to flow into the bore hole.
There has been a severe problem with service life of the tool joints since approximately 95 percent of the surface of the earth is composed of silicious materials which are very abrasive and which cause considerable wear on the tool joints, particularly the box member of the tool joint while the drill's string is being rotated thereby rubbing the enlarged box portion against the earth and thus shortening the life of the tool joint.
There have been numerous attempts to provide hardfacing on the box member of the tool joint. For a description of prior art hardfacing for tool joints, reference is made to U.S. Pat. No. 4,256,518, the composite catalog of oil field equipment and services, 1976/77 edition, at pages 3216-19 and pages 4994-5; U.S. Pat. No. 3,067,593. Also, for the use of hardfacing materials, such as tungsten carbide particles to form a hardened surface at a tool joint to increase wear resistance, reference is made to U.S. Pat. No. 3,989,554 issued Nov. 2, 1976 and then the history of oil well drilling by J. E. Brantly published in 1971 by the book division of Gulf Publishing Company, Houston, Texas. Also, reference is made to U.S. Pat. Nos. 2,259,232; 2,262,211; 4,431,902; and 4,942,059 which illustrates various prior art ways to hardface tool joints.
Historically, and in practice, tool joints on drilling pipe such as used in drilling oil and gas wells have been faced at the bottom of the box end with tungsten carbide to resist the abrasion of the rock earth in the drill hole on the tool joint. This has three disadvantages. Tungsten carbide is expensive, it acts as a cutting tool to cut the well casing in which it runs, and the matrix is a soft steel which erodes away easily to allow the carbide particles to fall away.
In most industries, the metal components which make up the structure and equipment of a given plant must have integrity, which means being free of any kind of cracks since these might be expected to progress through the piece and destroy the part.
When the loss of human life may be involved or when great property damage may result, the requirements for integrity are particularly strict. Examples are pressure vessels in the process industries, structural members in buildings and bridges and down hole drilling equipment in the oil and gas industry.
Hardfacing materials harder than silicious earth materials are brittle and crack. In the 50 year history of hardfacing tool joints of drilling pipe, no facing which cracked has been used in practice prior to the development of the present invention.
It would be highly desirable to provide hardfaced drilling tool joints and methods of hardfacing such tool joints which provide a surface harder than silicious earth particles, and although it cracks is satisfactory for use on tool joints providing longer wear life than at present and at the same time does not damage or cut the casing in the well bore.